High-temperature dust formation in carbon-rich astrophysical environments

TL;DR

This study experimentally investigates high-temperature dust formation in carbon-rich environments, validating thermodynamic models and exploring how pressure influences dust mineralogy, with implications for understanding cosmic dust in astrophysical settings.

Contribution

It provides the first experimental high-temperature condensation sequence for carbon-rich gases, validating kinetic models and predicting dust mineralogy in astrophysical environments.

Findings

Crystallized carbides, silicides, nitrides, sulfides, oxides, and silicates were modeled accurately.

Pressure significantly influences dust chemistry and mineralogy.

Iron silicide formation is unlikely in certain astrophysical environments.

Abstract

Condensation processes, which are responsible for the main chemical differences between gas and solids in the Galaxy, are the major mechanisms that control the cycle of dust from evolved stars to planetary systems. However, they are still poorly understood, mainly because the thermodynamics and kinetic models of nucleation or grain growth lack experimental data. To bridge this gap, we used a large-volume three-phase alternating-current plasma torch to obtain a full high-temperature condensation sequence at an elevated carbon-to-oxygen ratio from a fluxed chondritic gas composition. We show that the crystallized suites of carbides, silicides, nitrides, sulfides, oxides and silicates and the bulk composition of the condensates are properly modelled by a kinetically inhibited condensation scenario controlled by gas flow. This validates the thermodynamic predictions of the condensation sequence at a high carbon-to-oxygen ratio. On this basis and using appropriate optical properties, we also demonstrate the influence of pressure on dust chemistry as well as the low probability of forming and detecting iron silicides in asymptotic giant branch C-rich circumstellar environments as well as in our chondritic meteorites. By demonstrating the potential of predicting dust mineralogy in these environments, this approach holds high promise for quantitatively characterizing dust composition and formation in diverse astrophysical settings.